WASHINGTON (CNN) -- A decorated Marine colonel turned anti-war congressman has said Marines killed at least 30 innocent Iraqi civilians "in cold blood" in Haditha in November, suggesting the death toll may be twice as high as originally reported.

Rep. John Murtha, D-Pennsylvania, told reporters Wednesday that he got his information from U.S. commanders, who said the investigation will show that the Marines deliberately killed the civilians.

The U.S. Marine Corps has declined to comment on the report, which initially stated that 15 were killed.

"There was no firefight. There was no IED that killed these innocent people. Our troops overreacted because of the pressure on them, and they killed innocent civilians in cold blood," Murtha said.